National Mineral Resources Assessment, Using Geochemical Block Concept

The Sketch of the paper1 Two questions be answered: one is how to assess national mineral resource; another one is where are the favorable places of the occurrence of large to giant ore deposits.2 Methods and technique: using geochemical block concept;3 Procedures: using a case study of national Tin resource assessment by using methodology of Geochemical Block to demonstrate how to resolve these two questions in detail.The concept and methodology of Geochemical BlocksThis paper gives an overview and examples by using Geochemical Block Concept in mineral resources assessment in China. The Geochemical Block concept were developed by prof. Xie, by study the flood of high quality data obtained in China' s national geochemical mapping program (RGNR) carried out for already 24 years over more than 6 million km~2 of China' s territory, he has found more broad geochemical patterns other than dispersion halos and dispersion trains e. g. geochemical regions, geochemical provinces, geochemical megaprovinces and geochemical domains. They are the surface expressions of large blocks of rock with higher metal contents. So the concept of Geochemical Block expresses the giant rock blocks with high content of one or more elements within the upper earth's crust, they are the net results of the earth' s original heterogeneity, the distribution and redistribution of metals during the evolution of earth up to the present days and provide large metal endowments necessary for the formation of large to giant ore deposits. These blocks can be delineated by the methods of exploration geochemistry. The regions, which located within or surrounding the Geochemical blocks, are favorable targets for finding new large to giant ore deposits of different types, and important new discoveries have been already obtained in some regions in China.So the principle objective of the Geochemical Block Method is to outline the favorable regions that content huge amount of metals necessary for large or giant ore deposit formation, and estimate the probable amounts of undiscovered mineral resources to a depth of 1 km below the earth's surface. In these areas, geological and geophysical information can be utilized to help identify the more detail area permissive for the occurrence of undiscovered mineral deposits. In a selected research population, the procedure of this system is that:1 determination of each metal's threshold value for delineating its geochemical blocks;2 delineation of the geochemical blocks in this area;3 estimation of the Mineralization Coefficients (MC) in the well explorated geochemical blocks;4 calculation the parameters of every block: including size, mean of metal's content, metal endowment and metal amount per km~3; and to construct a family tree for demonstrating block's internal structure;5 estimation of the potential resource in every block, and selection of prospective area for the occurrence of large to giant ore deposit;6 reduction of the prospective area by integrating geological and geophysical information. It was believed that, through these steps above, the mineral exploration target could be reduced within a very limit area, with high probability of the occurrence of undiscovered deposits.Case studyA case study of National Tin potential resource assessment by using Geochemical Block methods was demonstrated in this paper.The average metal values of stream sediment samples within each 1:25 000 quadrangle map composed the dataset for calculating the threshold of each metal. The value of the threshold for delineating China Sn geochemical blocks is 6 ppm. And also, the contour level of 6, 8, 10, 13, 16, 20 ppm was determined to delineate the geochemical sub-block.Total about 51 Sn geochemical blocks were delineated in China. These blocks mainly distribute in South China, South-west Yunan, Xizang and East Neimenggu, the size of the largest Sn geochemical block is about 300 000 km~2, and its total tonnage of Sn is about 12 billion tons (given a 1000 m thickness). And 181 known Sn deposits from total 317 in China are located within No. 1 block in South China, it showss clearly that the large Sn endowment is the prerequisite for the large to giant Sn ore camp formation.Through the spatial analysis of the distribution of known Sn deposits and Sn geochemical blocks, it's found that there is a high probability for the Sn deposits to occurr within blocks. The numbers of Sn deposits located within Sn geochemical blocks to total Sn deposits in China is 82.6%, among these deposits, for large Sn deposits, is 92%. Also an analysis of spatial relationship between Sn geochemical blocks and geological setting has been done, and it is found that the favorable geological settings of the occurrence of Sn blocks are Mesozoic granite, Mesozoic calcareous sediment rocks in turn.The geochemical block mineralization coefficients (MC) for national Sn resource assessment was determined by anatomizing five well explorated blocks or sub-blocks. At 8 ppm concentration level, the MC is 0.1232% (including sand-type Sn deposits) and 0.0736%, and at 10 ppm concentration level, the MC is 0.1252% (including sand-type Sn deposits) and 0.0766%.Using these MC, 6 important Sn geochemical blocks are analyzed in detail, and the potential Sn resource in each blocks is estimated. Several prospective regions for searching large to giant Sn deposits, such as Huanan Yue-Gui-Xiang-Gan Area, Xizang-to-Yunnan Sanjiang region, are outlined.At 8 ppm concentration level, the national potential Sn resources is estimated, the total amount of Sn is about 17.98 million tons (including sand-type Sn deposits) and 13.21 million tons; at 10 ppm level, the number is 14.02 million tons (including sand-type Sn deposits) and 10.37 million tons.